Fluid sprinkling – spraying – and diffusing – Rigid fluid confining distributor – Including flow passage liner
Reexamination Certificate
2000-01-26
2003-04-15
Mar, Michael (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Rigid fluid confining distributor
Including flow passage liner
C239S589000, C029S888400, C029S557000
Reexamination Certificate
active
06547167
ABSTRACT:
BACKGROUND OF THE INVENTION
Contemporary fluid dispense systems are well suited for dispensing precise amounts of fluid material at precise positions on a substrate. A pump transports the fluid to a dispense tip, also referred to as a “pin” or “needle”, which is positioned over the substrate by a micropositioner, thereby providing patterns of fluid on the substrate as needed. As an example application, dispense tips can be utilized for depositing precise volumes of adhesives, for example, glue, resin, or paste, during a circuit board assembly process, in the form of dots for high-speed applications, or in the form of lines for providing underfill or encapsulation.
FIG. 1
is a perspective view of a conventional dispense tip
24
. The dispense tip
24
includes a body
26
and a hollow neck
28
. The body
26
attaches to a pump
22
, for example by means of a thread, which controls the amount of fluid to be dispensed. The neck
28
is typically a hollow cylinder having a first end
31
which is positioned to overlap with an aperture formed in the body
26
, and a second end
30
at which the fluid is dispensed.
As shown in the close-up perspective view of
FIG. 2
, the neck
28
is formed by rolling a flat portion of machined metal into a cylindrical form. A seam
40
is welded along the longitudinal axis, to seal the edges of the flat portion, using conventional seam welding techniques. In precision tips, the inner diameter of the opening at the second end
30
may be on the order of 0.030 inches in diameter. The thickness of the walls
32
may be on the order of 0.010 inches. A hole
29
is bored into the tip body
26
, and the neck
28
is aligned with, and pressed into, the hole. As a consequence of rolling and welding, the inner diameter of the neck is often unpredictable due to inner collapse.
When fluid is released at the opening
30
, a high degree of surface tension on the substrate is desired, such that the substrate receives and pulls the fluid from the tip
24
. It is further desirable to minimize the surface tension of the neck
28
interface such that when the pin retracts from the substrate, dispensed fluid properly remains on the board. However, a certain degree of surface tension in the neck exists due to the thickness of the walls
32
of the neck
28
at the opening
30
.
It has been observed that the surface tension, or “land”, at the opening
30
of the neck
28
can be reduced by tapering the outer diameter of the neck
28
to a sharp point. As shown in
FIG. 3
, the distal end
30
of the neck
28
is sharpened using a surface grinder
42
. The neck
28
is positioned perpendicular to the motion of the grinder
42
as shown, to thereby generate a taper
36
, or bevel, on the distal end of the neck
28
. The tapered portion
36
varies in thickness from the outer diameter of the neck
28
at position
37
A to a sharpened point
37
B at the opening
30
. For the example given above, by providing a taper
36
, the amount of land at the opening may be reduced from 0.010″ of contact about the perimeter of the opening, to 0.001″ of contact. In this manner, the surface tension at the junction of the pin and fluid is highly reduced, leading to a higher degree of dispensing precision.
As shown in the close-up perspective view of
FIG. 4
, as a consequence of formation of the taper
36
in the manner described above, with the neck
28
positioned substantially perpendicular to the grinding wheel
42
, tooling scars, in the form of radial rings
38
, can form on the taper
36
due to surface variations in the grinding wheel
42
. These rings
38
provide ledges or shelves that can lead to additional surface tension on the taper
36
, which, in turn, capture fluid material when the tip is released from the substrate following a fluid deposit. This, in turn, can cause fluid to be dispensed inconsistently on the substrate during subsequent deposits, leading to inaccurate results.
SUMMARY OF THE INVENTION
The present invention is directed to a tapered dispense tip grinding method, and a dispense tip processed according to such a method, that overcome the aforementioned limitations associated with conventional techniques. In the present invention, the tip is presented to the grinding wheel in a longitudinal orientation - the longitudinal axis of the neck of the tip is substantially aligned with the direction of movement of the grinding wheel. In this manner, the taper is formed without the radial rings of conventional techniques, thereby providing a tip with further-reduced surface tension and therefore increased dispensing precision capability.
In a second aspect, the present invention is directed to an electropolishing technique whereby a beveled tip is electropolished to further buff, or remove, tool marks generated during bevel formation. In this manner, burrs and pits are removed from the surfaces of the tip. This aspect is applicable to treatment of both conventional laterally-ground and the inventive longitudinally-ground tapered tips. Electroplating may further be applied to external and internal tip surfaces to enhance surface lubricity.
In a third aspect, the present invention is directed to a dispense tip formed in a solid unitary piece, machined from stock. By machining the neck opening, potential inner collapse of the neck due to rolling as in prior configurations is avoided. Furthermore, alignment of the neck with the body of the tip is unnecessary and complicated assembly procedures are thereby avoided. The unitary tips further offer the advantage of a robust neck, avoiding the need for bonding of the neck to an alignment foot. Because of the added robustness, the unitary tips are more amenable to deployment with longer-length necks than conventional configurations.
In a preferred embodiment of the third aspect, the neck is of a first inner diameter along a majority of its length, and of a second inner diameter proximal to the opening, the first inner diameter being greater than the second inner diameter. This configuration allows for delivery of the dispensed fluid to the opening at a relatively low pressure, as compared to conventional tips having a single, narrow diameter over their lengths, and is especially attractive to dispensing applications that require smaller diameter tips.
A preferred embodiment of the third aspect of the present invention comprises a unitary fluid dispense tip. The tip includes an elongated cylindrical neck having a longitudinal axis. A bore is machined in the neck centered at the longitudinal axis, the bore having an input end and an output end. The input end of the bore has an inner surface of a first inner diameter and the output end of the bore has an inner surface of a second inner diameter, the first inner diameter being greater than the second inner diameter. An inner taper is machined in the bore such that the inner surface of the bore transitions gradually from the first inner diameter to the second inner diameter.
The inner taper is preferably proximal to the output end of the neck, and is preferably formed at an angle of approximately 20-40 degrees relative to the longitudinal axis of the neck. The neck is preferably formed with a body about the input end of the neck, the body including a funnel adapted for delivering fluid to the input end of the neck. The body may optionally be formed separately from the neck, in which case the body and neck are preferably coupled via press-fitting, bonding, or welding. An alignment foot may be coupled to the body so as to provide a vertical gap below the neck during a dispensing operation. Multiple necks may be mounted to the body, in which case the funnel is adapted for delivering fluid to the multiple input ends of the multiple necks.
A liner sleeve may be inserted in the neck of the dispense tip in order to reduce material flow for low-viscosity materials. The sleeve may comprise, for example, Teflon™ tubing, inserted by a sleeve insertion tool adapted to push the tubing into the neck, and removed by a sleeve removal tool.
In a fourth aspect, the present inventio
Hwu Davis
Mar Michael
Mills & Onello LLP
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